Articulated carriage tilting dumping vehicle

ABSTRACT

An articulated carriage with tandem sections is supported and guided by a track for movement to a location above a steelmaking furnace, preferably of the basic oxygen type. A forward carriage section carries a charge container and a following carriage section drives the carriage along the track. Forward movement of the front section is stopped above the furnace and continued movement of the trailing section jackknifes the carriage, tilting the front section and charge container forward. A portion of the track above the furnace is angularly inclined downwardly relative to a preceding portion of the track to initiate tilting of the front section of the carriage.

United States Patent [72] Inventors Klaus W. Forster Brecksville; DonaldW. Schaper, Alliance, both of Ohio [21] Appl. No. 847,766 [22] FiledJune 5, 1969 [2 3] Division of Ser. No. 671,784, Sept. 29, 1967,

Pa No- 491, 2-v [45] Patented Oct. 19, 1971 [7 3] Assign ee KermaCorporation Alliance, Ohio [54] ARTICULATED CARRIAGE TlLTlNG DUMPING261,261.],29 R, 241,261,261 A;214/18, 188C, 18 PH, 19, 58,62, 64, 103

Primary ExaminerArthur L. La Point Assistant ExaminerHoward BeltranAttorney-Watts, Hoffman, Fisher & Heinke ABSTRACT: An articulatedcarriage with tandem sections is supported and guided by a track formovement to a location above a steelmaking furnace, preferably of thebasic oxygen type. A forward carriage section carries a charge containerand a following carriage section drives the carriage along the track.Forward movement of the front section is stopped above the furnace andcontinued movement of the trailing section jackknifes the carriage,tilting the front section and charge container forward. A portion of thetrack above the furnace is angularly inclined downwardly relative to apreceding portion of the track to initiate tilting of the front sectionof the carriage.

PATEN-TEUucT 19191: 3.613.602

SHEET 1 BF 4 a INVENTO KLAUS w. FORSBIER DONALD W.SCHAPER BY W)ATTORNEYS.

SHEETEDF 4 PATENTEnnm 19 I97] RSTFER DONALD W SCHAP R Qiafi KLAUS w. F5

g ATTORNEYS.

PATENTEDDBI 19 mi 3,613,602

SHEET 30F 4 INVENTORS KLAUS W. FORSTER DONALD W. SCHAPER ATTORNEYS.

ARTICULATED CARRIAGE TILTING DUMPING VEHICLE RELATED APPLICATIONS Thisapplication is a division of U.S. application, Ser. No. 671,784, nowU.S. Pat. No. 3,497,089, issued Feb. 24, 1970, filed Sept. 29, 1967, forApparatus and Method for Charging a Furnace.

FIELD OF INVENTION This invention relates to apparatus for handling anddumping containers, especially those used for charging a steelmakingfurnace of the basic oxygen type.

SUMMARY OF INVENTION The present invention provides economical apparatusthat will handle and dump a container, especially one containingmaterial to be charged, into a steelmaking furnace with minimal directoperator control. An articulated carriage movable along the trackcarries a container, such as a ladle, and automatically tilts thecontainer at a proper location to discharge its contents, for example,into a furnace. The tilting of the container is accomplished by themovement of the carriage along the track, eliminating the need forseparately controlled means for'conveying the container and tilting thecontainer to discharge its contents. Also, the rate at which thecontents of the container, such as molten iron, is discharged form thecontainer can be controlled. One of the principle objects of thisinvention is to provide a novel articulated carriage for carrying acontainer of material to be dumped at a predetermined location along aguided track, wherein the carriage is tilted by changing the relativeangular relationship of two sections of the carriage about a'horizontalaxis in response to movement of the carriage along the track in order todump the contents of the container.

It is another object of this invention to provide a carriage, as

' described above, which includes a pivotal support for the container topermit the container to remain vertical while the carriage travel alonginclined portions of a track, and stop members on the carriage thatlimit the pivotal movement of the container relative to the carriage sothat the container is tilted when the carriage is tilted beyond apredetermined angle.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription of the preferred embodiment described with reference to theaccompanying drawings, in which:

FIG. 1 is a diagrammatic, partial elevational view showing a carriageand track constructed and arranged in accordance with the presentinvention and the adjacent environment of a steelmaking furnace;

FIG. 2 is a top plan view of the horizontal track portion and carriageof FIG. 1;

FIG. 3 is a longitudinal sectional view through a track member of FIG.2, taken along the line of 3-3 and looking in a the direction of thearrows, and showing the carriage in side elevation;

FIG. 4 is an end elevational view taken from the right-hand side of FIG.3;

FIG. 5 is a sectional view taken along the line 4-4 of FIG. 2 andlooking in the direction of the arrows, showing details of the ladle carof the carriage;

FIG. 6 is a side elevational view of the ladle car of FIG. 2 withportions broken away, showing constructional details of a ladle ringcarried by the ladle car;

FIG. 7 is a diagrammatic view of the ladle car and ladle of FIG. 6showing the manner in which the ladle ring and ladle can pivot relativeto the car;

FIG. 8 is a diagrammatic view similar to FIG. 7, showing the manner inwhich the ladle ring and ladle can pivot in an opposite directionrelative to the ladle car from the shown in FIG. 7;

FIG. 9 is a fragmentary side elevational view taken along a planesimilar to that of FIG. 3 through an inclined portion of the track toillustrate a safety ratchet carriedon the carriage;

FIG. 10 is a partial side elevational view with a portion of one trackguide member removed, illustrating the position of the carriage andladle at the terminal end of the track adjacent a furnace, prior totilting the ladle;

FIG. 11 is a side elevational view similar to FIG. 10, illustrating themanner in which the ladle car and ladle are tilted to introduce a chargeto a steelmaking furnace;

FIG. 12 is a partial side elevational view, with a part in section ofthe terminal end of a track guide member viewed from the inside,illustrating details of a stop member for engaging and holding an axleof the carriage, and specifically showing the manner in which a portionof the axle is received priorto tilting of the carriage; and

FIG. 13 isa partial elevational view similar to FIG. l2tillus tratingthe manner in which an axle portion of the carriage is retained by thestop member when the ladle car is tilted.

A general arrangement of a furnace charging apparatus constructed inaccordance with. the present invention is shown in FIG. 1 of thedrawings. The apparatus is shown in connection with a conventionalsteelmaking furnace vessel 20, and includes a track 22 and anarticulated carriage 24 that carries a ladle 25 along the track from aloading area at which the carriage is shown in solid line, remote fromthe furnace, to a charging station above the furnace vessel'20, wherethe carriage and ladle are shown in phantom.

The furnace vessel 20 is of the type used in the basic oxygen processand is shown tilted to receive a furnace charge. The furnace can befurther tilted after the charge is processed to discharge its contentsinto one or more ladles 26 and slag pots 28, which are carried ontransfer cars 29, 30, respectively, on a track 31 at a level below thefurnace vessel 20.

The track 22 that carries the carriage 24 includes a horizontal portion22a at a first level beneath a platform support or floor 34, an upwardlyinclined portion 22b extending from the horizontal portion to a higherlevel above the furnace vessel 20, and a terminal portion 22c that isinclined downwardly directly adjacent and above the furnace vessel 20when'the furnace vessel is tilted as shown in FIG. I to receive acharge. A molten iron transfer ladle 36, of the torpedo type, is shownon tracks 38 that extend across the track 22 at the level of theplatform or floor 34 above reinforcing beams 39. The transfer ladle 36can be moved over the track 22 at the loading area to transfer moltenpig iron to the ladle 25, which is then carried by the carriage 24 alongthe track 22 and charged into the furnace vessel 20.

The carriage 24 is in two sections and comprises a ladle carriagesection or car 42 and a drive carriage section or car 44. The twocarriage sections or cars are pivotally connected together in tandem bya horizontal transverse axle shaft 46 and are supported on three pairsof wheels 47, 48, 49 that ride on the track 22.

The track 22 is constructed of two laterally spaced, side-byside, guidemembers 52, 54 in the fonn of channels in which the pairs of wheels 47,48, 49 of the carriage 24 ride. The guide members 52, 54 are mirrorimages of each other and the structure mounted on the guide members isidentical for each; therefore, only the guide members 52 and associatedstructure will be described in detail. Corresponding parts on the guidemember 54 are referred to by corresponding reference numerals,designated with a prime.

The guide member or channel 52 is formed of a vertical web 56 and upperand lower flanges 58, 59 extending inwardly of the track. A rail 62 forsupporting the wheels of the carriage 24 is mounted on the upper surfaceof the lower flange 59 and a chain 64, which functions as a rack, isfixed to the lower surface of the upper flange 58. The chain 64 isofiset laterally outward with respect to the rail 62, as bent shown inFIGS. 2 and 4. At the terminal end 22c of the track, where the track isinclined downward, the upper flange is open at 65. (See FIG. I and thecorresponding portion 65 of the guide member 54 in FIGS. and 11.) Theopen portion 65 is located directly over the rail 62 and inwardly of thechain 64, so that the chain 64 follows the contour of the guide memberwhile the open portion permits the center pair of wheels 48 of thecarriage 24 to move out of the guide channels 52, 54 when the ladle carreached the end of the track.

A stop member and latching device 66 is located in the channel membersat the terminal end of the track, and serves to stop the front portionof the carriage 24 and secures it against movement along the track ineither direction once the ladle car section of the carriage is tiltedrelative to the track, in a manner to be further described subsequently.The device 66, as shown in detail in FIGS. 12 and 13 is in the form of aplate secured to the inside of the vertical web of each guide member.The plate has a slot 67 having upper and lower edges 67a, 67b thatconverge to a minimum gap at 67C. The slot 67 terminates in a circularconfiguration 67d larger in diameter than the width of the gap 67c andwhich will receive the axle of the front wheels 47 of the ladle car.

The ladle car 42 has a frame 70 that is U-shaped in plan and formed ofopposite side portions 70a, 70b and a connecting front portion 70c. Atransverse front axle 72 is fixed in the front portion 700 of the frameand rotatably supports two wheels 47a, 47!: located outwardly of theframe 70. End portions 72a, 72b of the shaft 72 extend beyond the wheels47 and are the full diameter of the shaft longitudinally of the car butare smaller in the direction of the car height. This constructionfacilitates latching or keying the front axle in place at the terminalend of the track because the end portions 72a, 72b will pass through thegap 670 of the slot 67 in the stop member and latching device 66 whenthe carriage is aligned with the track. The end of the slot thencontacts the axle ends, acting as an abutment to stop forward movement.Once the ladle car is tilted, as shown in FIG. 13, the shaft 72 rotateswith the car and the end portions 72a, 72b cannot move back through thegap 670 from the circular portions 67d of the latching devices 66.

The horizontal transverse shaft 46 about which the ladle car 62 anddrive car 44 pivot relative to each other, is rotatably supported at theopposite end of the ladle car from the axle 72. Wheels 48a, 48b arerotatably supported on the carriage by this shaft and are located tothe'outside of the frame 70, aligned with the pair of wheels 47.

A ladle ring 75 is pivotally secured to the ladle car 42 and supportsthe depending ladle 25 in which molten iron is normally carried. Theouter periphery of the ladle ring 75 is generally rectangular in plan,as shown in FIG. 2. Stud shafts 78, 79 extend from opposite sides of theladle ring, are pivotally received in the side frame portions 70a, 70bof the ladle car and support the ladle ring for pivotal movementrelative to the ladle car about an axis parallel with the axle 72 andpivot axle 46. A stop member 82 in the form of a rectangular blockextends from the ladle ring 75 on each side, directly beneath the studshafts 78, 79. The stop members 82 extend into wedge-shaped recesses 84,85 (FIGS. 2, 3 and 5) formed on opposite inside surfaces of the frameportions 70a, 70b of the ladle car. Each recess has inclined surfaces84a, 84b and 85a, 85b respectively, which form an apex adjacent the studshafts and function as inclined abutment surfaces that cooperate withthe stop members 82 when the ladle car is inclined beyond a given anglewith the horizontal.

The manner in which the ladle and ladle ring freely swing within thelimits of the abutment surfaces so that the ladle ring is normallymaintained in a horizontal position is best illustrated in FIGS. 6, 7and 8. The ladle car 42 is illustrated in a horizontal position in FIG.6, corresponding to an orientation along the track section 220. In FIG.7, the ladle car is shown at an angle incline with the horizontal, aswhen the ladle car is moved up the inclined portion 22b of the track 22.FIG. 8 illustrates the angle of the ladle car 42 when supported by thetrack at the terminal portion 22C. In each of the positions shown, theladle remains level. It will be apparent from FIG. 8 that furthertilting of the ladle car 42 in a counterclockwise direction about theforward axle 72 will tilt the ladle 76 by virtue of the cooperationbetween the stop member 82 and the inclined surfaces 84a, 85a whichlimit relative pivotal movement between the ladle ring and car once thecar is tilted to the position shown in FIG. 8.

The drive car 44 is attached in tandem behind the ladle car 42 by thepivot axle 46 and is power driven to move the ladle car along the track22 between the loading station and charging station and to tilt theladle car and ladle at the charging station. The drive car 44 includes aframe 88 having longitudinally extending side portions 88a, 88b andcross beams 88c, 88d. The side portions 88a, 88b extend forwardly of thecrossbeam 880 and are connected to the pivot axle 46 so that the axle 46can rotate relative to the frame 88. The side frame portions 88a, 88balso extend rearwardly of the cross frame member 88d and are spanned bya flat body portion 89 that serves as a support for a drive unitindicated generally at 90.

Two short axle shafts 92, 94 extend through the side frame portions 88a,88b respectively behind the crossbeam 88d and are journaled in the sideframe for rotation. A wheel 49a is secured to the axle shaft 92 and awheel 49b is secured to the axle shaft 94. These wheels are aligned withthe other wheels 47, 48 and ride on the rails 62, 62'. Each shaft 92, 94extends outward, beyond the wheel. A sprocket 96 is fixed to the outerend of the shaft 92, and a sprocket 98 is fixed to the outer end of theaxle shaft 94. The inner ends of the axle shaft 92, 94 are respectivelydriven by gear trains in housings 100, 102. Within each of thesehousings a driven gear (not shown) is secured to the inner end of therespective axle shaft, and an intermediate idler gear 104 connects thedriven gear to a drive gear 106 (both shown in dotted lines in FIG. 3).The drive gear 106 associated with axle 92 is driven by a shaft 108 froman electric motor 112. The corresponding drive gear associated with theaxle 94 is driven by a shaft 109 from an electric motor 113. The driveshafts of each electric motor are axially aligned and connected by acoupling 116 between the two motors to assure that both drive at thesame speed. A solenoid actuated brake 118 is provided on the shaft 108,and a similar brake 119 is provided on the shaft 109. The brakes 118,119 provide a convenient means for maintaining the carriage 24 in fixedlocation, especially when the ladle 25 is being filled with a furnacecharge. Normally the motors 112, 113, in addition to driving thecarriage, are used to control the speed of the carriage 24 when it movesdown the inclined track section 22b.

A safety rachet 122 is carried by the drive car 44 (FIG. 3

and 9), With this to cooperate with the chain 64 to prevent uncontrolledmovement of the carriage down the inclined track portion 22b. The rachetmechanism consists of a pawl 123 pivoted on a shaft 124 extendingtransversely through and journaled in the frame portion 880. Acounterweight arm 126 is secured to the shaft 124 to bias the pawl 123into contact with the chain 64. A solenoid actuator 128 is connectedwith the counterweight arm 126 to pivot the pawl 123 out of contact withthe chain. With this arrangement, the pawl 123 biased by thecounterweight arm 126 permits the carriage 24 to move in a forwarddirection from the loading station to the charging station whilepreventing movement of the carriage in the opposite direction, shouldthere be a power failure that would disable the drive mechanism. When itis desired to move the carriage from the charging station back to theloading station, the solenoid 128 is energized, pivoting the pawl out ofcontact with the chain and permitting movement of the carriage in theopposite direction.

Electric current to operate the motors 112, 113, brakes I18, 119 andsolenoid 128 of the drive car 44 is supplied in a conventional manner(not shown), as by a conductor or third rail-associated with the trackand a collector associated with the carriage, or by flexible cablesconnected directly from a source of power to the drive car.

In operation, the carriage 24 is first positioned at the load ingstation, where it is shown in solid line in FIG. 1. The ladle 25 isfilled with a furnace charge, such as molten pig iron from a transferladle 36. While the carriage is located at the loading station, thebrakes 118, 119 are actuated to prevent movement of the carriage. Oncethe ladle is filled with molten metal, the brakes are released and theelectric motors I12, 113 are energized to rotate the drive shafts 108,109 and the sprockets 96, 98 in a clockwise direction as viewed in FIG.3. By virtue of the engagement of the sprockets 96, 98 with the chains64, 64', the carriage is moved along the rails 62, 62' of the guidemembers 52, 54 and up the inclined portion 22b of the track 22 towardthe charging station. During this movement of the carriage, the solenoid128 controlling the pawl 123 of the safety rachet 122 is deenergized sothat the counterweight arm 126 holds the pawl in contact with the chain64.

As already indicated, at the loading station the ladle car and ladle areas shown in FIG. 6. When the carriage is moved up the inclined section22b of the track, the car and ladle pivot relatively to the positionshown in FIG. 7, and when the carriage first reaches the chargingstation, the ladle car is positioned in the track portion 22b in therelationship shown in FIG. 8. The position of the entire carriage atthis time is shown in FIG. of the drawings.

As shown in FIG. 10, when the carriage first reaches the terminal end ofthe track 22 the ladle car 42 is inclined downward and the drive car 44is inclined upward, the two being pivoted about the pivot axle 46.Extending ends 72a, 72b of the front axle shaft 72 engage the stopmember 66 and prevent further forward movement of the front of the ladlecar. Continued rotation of the drive sprockets 96, 98 causes the drivecar 44 to continue its movement up the inclined portion 22b of thetrack. The intermediate pair of wheels 48 leaves the track and continuesin a generally upward direction through the openings 65, 65 in the trackguide members 52, 54. This continued movement of the drive car causesthe ladle car to pivot in a forward direction about the front axle 72 tothe position shown in FIG. 11 of the drawings. Because the stop members82 on the ladle ring 75 prevent the ladle from pivoting clockwise, asviewed in FIGS. 10 and 11, relative to the ladle car once the car is inthe position shown in FIG. 10, the ladle is tilted with the car asindicated by the arrow A to discharge the contents of the ladle into thefurnace vessel 20.

During the tilting of the ladle car 62, the front axle shaft 72 rotatesrelative to the track and is thereby secured against movement along thetrack by the narrow gap 67c of each stop member and latching device 66.This prevents the front end of the ladle car from moving backward alongthe track once the car is pivoted beyond the vertical.

Once the drive sprockets 96, 98 of the drive car reach the positionalong the track shown in FIG. 11, a limit switch (not shown) stops theoperation of the electric motors 112 and 113. After a short time delayto allow the ladle to empty, the motors 112, 113 are reversed, thesolenoid 128 to the safety rachet 122 is energized and the drive car 44is moved back along the track 22 toward the loading station. Thismovement first tilts the ladle car back to the track, to the positionshown in FIG. 10, and then move the entire carriage 24 to the positionshown in FIG. 1, where the ladle 25 can receive a subsequent charge.

From the foregoing, it will be appreciated that the present inventionincludes the provision of a reliable and essentially automatic inclinehoist which (I) eliminates the need for a separate guide track toseparately cause tilting and pouring of the charge carrier, (2) controlsthe rate at which the charge is poured by the speed of movement of thecarriage and (3) is relatively simple and reliable in operation.

While a preferred embodiment of the present invention has been disclosedin detail, it will be readily appreciated that various modifications oralternations may be made therein without departing from the spirit andscope of the invention.

We claim:

1. An articulated carriage for carrying a container along a guidingtrack, said carriage comprising: first and second carriage sections;pivot means securing said first and second carriage sections together intandem for relative angular movement about a first transverse axis;three pairs of wheels spaced along the length of the carnage meansconnecting a first pair of the wheels to the first carriage sectionadjacent one end of the carriage for rotation about a second axisparallel with the first axis; means connecting a second pair of thewheels to the second carriage section adjacent the other end of thecarriage for rotation about a third axis parallel with the first axis;means connecting a third pair of the wheels to the carriage sectionscoaxial with the first axis; a container support pivotally connected tothe first carrier section and abutment means on the first carriagesection engageable by said container support for limiting tilting of thecontainer support relative to the first carriage section.

2. An articulated carriage for carrying a container along a guidingtrack, said carriage comprising: first and second carriage section;pivot means securing said first and second carriage sections together intandem for relative angular movement about a first transverse axis,three pairs of wheels spaced along the length of the carriage meansconnecting a first pair of the wheels to the first carriage sectionadjacent one end of the carriage for rotation about a second axisparallel with the first axis, means connecting a second pair of thewheels to the second carriage section adjacent the other end of thecarriage for rotation about a third axis parallel with the first axis;means connecting a third pair of the wheels to the carriage sectionscoaxial with the first axis; a container support pivotally connected tothe first carriage section: a fixed abutment on the first carriersection engageable by said container support for limiting tilting of thecontainer support relative to the first carriage section; a drivesprocket on the second carriage section adapted to engage a rack alongthe guiding track; and power means carried by the second carriagesection to rotate the drive sprocket.

3. An articulated carriage for carrying a container with a charge for afurnace along a guiding track having first abutment means adjacent theend of the track and second abutment means spaced inwardly of the end ofthe track, said carriage comprising: first and second carriage sections;pivot means securing said first and second carriage sections together intandem for relative angular movement about a first transverse axis;three pairs of wheels spaced along the length of the carriage meansconnecting a first pair of the wheels to the first carriage sectionadjacent one end of the carriage for rotation about a second axisparallel with the first axis; means connecting a second pair of thewheels to the second carriage section adjacent the other end of thecarriage for rotation about a third axes parallel with the first axis;means connecting a third pair of the wheels to the carriage sectionscoaxial with the first axis; a container support pivotally connected tothe first carriage section; a fixed abutment on the first carriersection engageable by said container support for limiting tilting ofcontainer support relative to the first carriage; and a member on thefirst carriage section at the said one end of the carriage engageablewith the first abutment means along the guiding track, movable past thesecond abutment means along the guiding track when the first carriagesection of the carriage is aligned with the guiding track and engageablewith the second abutment means when the first carriage section is tiltedrelative to the track.

1. An articulated carriage for carrying a container along a guidingtrack, said carriage comprising: first and second carriage sections;pivot means securing said first and second carriage sections together intandem for relative angular movement about a first transverse axis;three pairs of wheels spaced along the length of the carriage meansconnecting a first pair of the wheels to the first carriage sectionadjacent one end of the carriage for rotation about a second axisparallel with the first axis; means connecting a second pair of thewheels to the second carriage section adjacent the other end of thecarriage for rotation about a third axis parallel with the first axis;means connecting a third pair of the wheels to the carriage sectionscoaxial with the first axis; a container support pivotally connected tothe first carrier section and abutment means on the first carriagesection engageable by said container support for limiting tilting of thecontainer support relative to the first carriage section.
 2. Anarticulated carriage for carrying a container along a guiding track,said carriage comprising: first and second carriage section; pivot meanssecuring said first and second carriage sections together in tandem forrelative angular movement about a first transverse axis, three pairs ofwheels spaced along the length of the carriage means connecting a firstpair of the wheels to the first carriage Section adjacent one end of thecarriage for rotation about a second axis parallel with the first axis,means connecting a second pair of the wheels to the second carriagesection adjacent the other end of the carriage for rotation about athird axis parallel with the first axis; means connecting a third pairof the wheels to the carriage sections coaxial with the first axis; acontainer support pivotally connected to the first carriage section: afixed abutment on the first carrier section engageable by said containersupport for limiting tilting of the container support relative to thefirst carriage section; a drive sprocket on the second carriage sectionadapted to engage a rack along the guiding track; and power meanscarried by the second carriage section to rotate the drive sprocket. 3.An articulated carriage for carrying a container with a charge for afurnace along a guiding track having first abutment means adjacent theend of the track and second abutment means spaced inwardly of the end ofthe track, said carriage comprising: first and second carriage sections;pivot means securing said first and second carriage sections together intandem for relative angular movement about a first transverse axis;three pairs of wheels spaced along the length of the carriage meansconnecting a first pair of the wheels to the first carriage sectionadjacent one end of the carriage for rotation about a second axisparallel with the first axis; means connecting a second pair of thewheels to the second carriage section adjacent the other end of thecarriage for rotation about a third axes parallel with the first axis;means connecting a third pair of the wheels to the carriage sectionscoaxial with the first axis; a container support pivotally connected tothe first carriage section; a fixed abutment on the first carriersection engageable by said container support for limiting tilting ofcontainer support relative to the first carriage; and a member on thefirst carriage section at the said one end of the carriage engageablewith the first abutment means along the guiding track, movable past thesecond abutment means along the guiding track when the first carriagesection of the carriage is aligned with the guiding track and engageablewith the second abutment means when the first carriage section is tiltedrelative to the track.